Before the present invention, sirens, bells, whistles and other noise emitting devices mounted on emergency vehicles produced high levels of sound to warn others as the emergency vehicle proceeded to an emergency scene. Unfortunately, the occupants of the vehicle, were exposed to potentially dangerous and injurious levels of sound. No known device other than the present invention is intended on focusing and reducing the warning sound in an interior cab of an emergency vehicle to acceptable levels and still adequately warn other non-emergency vehicles of the emergency vehicle's approach.
Most known devices, such as that described in U.S. Pat. No. 4,138,673 to Faust, are intended on improving the performance of a siren by producing a more piercing and effective sound. The present invention attempts to focus the sound to be effective in regard to the special area around the siren, particularly the vehicle it is positioned on.
Devices such as that described in U.S. Pat. No. 1,941,324 to Schirmer are only able to adjust or lessen the emitted sound but do nothing to focus the emitted sound in a simple manner, with few components and needing only minor calibration. The invention to Schirmer is particularly suited for building fire alarms allowing one signal device to be used in an number of applications. The vibrating horn uses a diaphragm which moves in a back and forth motion pushing and pulling on the air around it to produce sound. This rapid back and forth movement of sound producing air, can then be contained within the confines of the device by use of the baffle or damper. The sound is actually being generated by the sound generating device based on the air contained within the device. Regardless of the damper's position, the air contained within allows for this sound generation. The damper's only perceived function is to keep the movement of this air within the structure of the horn thus diminishing sound external to the sound device. The invention disclosed in Schirmer is different in both theory and application from the present invention.
The present invention affords the use of a single internal damper or baffle to reduce the emitted sound level and focus the sound away from the cab interior of an emergency vehicle. The damper limits the sound producing media, that being air from reaching the sound generating device thus limiting the device's sound producing potential. This is due to the vacuum-type effect at the point the damper placed. Schirmer's sound generating mechanism produces alternating positive and negative air pulses with its back and forth movement of the diaphragm thus not requiring a constant supply of fresh air to continue generating sound. Again, the present invention damper works in a vacuum type of environment when the sound device is in use and acts to limit air volume to a device that requires a constant "flow through" of air to produce sound.
Simply stated, Schirmer's dampers are used to contain an already generated sound from escaping the confines of the device, whereas the damper in the present invention is used to prevent the sound from being produced in the first place. The damper in the present invention does not contain the sound, but limits its production. Schirmer uses a no-air-out, no-sound-out theory. The present invention uses no-air-in, no-sound produced theory.
It should be noted that the sound generating devices for which the present invention was conceived, are all totally air "flow through" dependant devices. Unlike those shown in Schirmer, where the horn is not air "flow through" dependant as it reuses the same given volume of air it contains within.
The present invention has application not only to new sirens but also as a retrofit device on existing sirens. This is especially important in that numerous other sirens and general warning devices require that a new siren be purchased in order to reduce the sound emitted to meet government sound reduction standards.